This invention relates to an apparatus for examining at least one visual function in the eye of a test subject, including an optical apparatus portion which contains a relatively small-surface image-generating display screen for offering optical test objects at different angles with respect to the optical axis and a computer control for controlling the display screen. This invention further relates to a method which can be carried out by means of this apparatus. Apparatuses of this type are used for examining visual field defects or changes of the perception threshold per retina site under various marginal conditions, for example, examinations, such as perimetry or noise field campimetry. In addition, the apparatus permits the measuring of the visual acuity for the near and the distant region as a function of the brightness of the environment; the measuring of night vision under realistic conditions including blinding glare which may occur in traffic; color tests under adaptation conditions; and stereometric tests with the use of a binocular representation as well as examining strabismus including the determination of the strabismal deviation.
Methods for measuring the visual field are perimetry, campimetry or noise field campimetry. Perimetry discloses the sensitivity to light of any desirable point of the retina. The conventional device used in this case is an arrangement in the form of a spherical perimeter according to Goldmann etc. The test subject fixes on a fixing point offered in the center of the sphere. During this time, light spots are briefly offered to him at various locations within the sphere. He triggers a signal upon recognition. Computer-controlled perimeters are mostly used nowadays. In this case, the computer controls the projection of the testing spots with a site-dependent light intensity according to the physiological perception threshold of the retina at different sites within the sphere.
The method is also used in the form of campimetry. In this case, only the central field of vision of 30.degree. to 60.degree. eccentricity is tested by way of a video monitor. This type of testing is known, for example, from U.S. Pat. No. 4,634,243. In the case of campimetry, the patient fixes according to the same principle on a video monitor at a defined distance.
Noise field campimetry, as disclosed, for example, in European Patent Application 88112691.6, offers a noise field on the display screen in the manner of a television image "without reception". When viewing this noise field, in the case of existing visual field defects, the test subject can perceive these as a scotoma (brighter dark spot) in the noise field.
From European Patent Application EP 0 363 610A1, the projection of testing spots is known by way of a computer-controlled electromechanically deflectable projector, comprising a light source, a diaphragm and a lens. A certain miniaturization of the perimetric testing method is achieved by the fact that an optical imaging system with an enlarging characteristic is arranged between the light source and the observer point.
For testing the visual acuity, a method is known from U.S. Pat. No. 4,869,589 in which optical test objects are displayed on a computer-controlled monitor. In this case, the test is automated, in which case the patient can report his reaction to the system by way of a keyboard or a mouse.
For testing scotopic vision and sensitivity to glare, portable table top devices with eyepieces are known, for example, from German Patent document DE 30 03 588 C2 .
Testing apparatuses in the form of spectacles are known for measuring eye movements, for example, for measuring nystagmus; see, for example, German Patent document 38 25 789 C2 and European Patent document EP 0 456 166 A1 .
Current systems for examining visual functions have the problem that their dimensions are very large and the systems are also very expensive as different testing devices require high-expenditure arrangements of an examiner's display screen, a computer control, etc. In the case of the perimeter, the cupola alone has a diameter of between 60 cm and 100 cm. Campimeters are also very large systems as monitors, computer controls and distance devices in the form chin rests and forehead rests are required. Refractometers and other table-mounted units, which are usually based on an optical system of lenses and mirrors, are offered for testing visual acuity. The determination of the strabismal angle takes place by means of correcting prismatic glasses or on a "Harms Wall" (tangent scale according to Harms) measuring 2.5 m * 2.5 m. The majority of the apparatuses are very test-specific and are therefore suitable only for one or a few special tests so that additional equipment must be procured for other tests. Some systems can be operated only in darkened rooms while the brightness of the room cannot be adjusted or is difficult to adjust. Thus, marginal conditions, such as the room brightness, cannot be standardized and can therefore also not be reproduced in a precise manner.
The invention is based on the technical problem of providing an apparatus of the initially mentioned type which measures visual field defects at least in the central 30.degree. to 60.degree. field of vision and has a very compact construction, as well as on a method which can be carried out by means of this apparatus. It is another object to implement such an apparatus and the corresponding method such that, by means of it, subjective tests, such as the determination of the strabismal angle, can be objectified and vision tests can be standardized while the contrast and the room brightness are defined. Furthermore, only one apparatus of this type is to be used for carrying out different testing methods for which a respective separate apparatus had been required up to now.
These objects are achieved by an apparatus for examining at least one visual function in the eye of a test subject, including an optical apparatus portion which contains a relatively small-surface image-generating display screen for offering optical test objects at different angles with respect to the optical axis and a computer control for controlling the display screen. The optical apparatus portion is housed in a spectacletype and/or helmet-type carrier which can be mounted on the test subject and contains an optical imaging system in front of the display screen as well as by a method for examining a test subject by means of fixation, which can be implemented by means of the above-described apparatus. In the method, the position of the eyes by a measuring system and thereby the new position of a stimulus is adapted to the measure deviation from the fixation point. Because of the use of a relatively small-surface display screen in connection with an optical imagining system, a very compact construction is permitted. This allows the whole optical portion of the apparatus to be built in a spectacle-type and/or helmet-type carrier which can be mounted on the test subject, whereby the apparatus can be used in a very mobile and universal manner. As a result of supplementary sensory components, special illuminations as well as a light-proof construction, the functions are combined and standardized in apparatuses which previously were separate.
The method permits an automatic adaptation of the measuring system to changing positions of the eye so that it is not absolutely necessary that the test subject fix his eye always on the same point during a measuring operation of the examination of his visual functions. This also prevents measuring errors which are based on faulty subjective influences.
In this case, the examination of the visual field can be combined with other testing procedures, such as the perception testing after an adaptation to the dark, the measuring of visual acuity for distant vision and near vision, the measuring of the reaction speed of a test subject to an optical stimulus, the determination of strabismal angles, the testing for nyctalopia under traffic conditions with blinding by approaching lights as well as by means of color tests and stereometric tests. Thus, the invention combines different testing apparatuses in the miniaturized form of spectacles or of a helmet and the like. For reducing costs and saving space, it is preferable in this case that the control of the apparatus can be connected to personal computer systems in connection with a plug-in card.
Another advantage of the invention is the fact that the room in which the tests are to be carried out does not have to be darkened, as in the case of conventional methods, but the tests may take place in daylight under standardized brightness conditions.
Another advantage is the optimization of the visual field test in that not only a fixation control is permitted when the stimulus is offered but, in a further development of the invention, faulty fixations can be measured and can automatically be compensated when the stimulus is offered. This not only improves the procedure but also accelerates the test routine because no repetitive measurements have to be carried out.
In the following, the invention will be explained in detail by means of drawings representing a preferred embodiment.